We propose a research project in which we shall continue to evolve our method of hydrogen calorimetry so as to determine heats of hydrogenation of biochemically interesting molecules with increased sensitivity and accuracy. These goals are important if one wishes to study relatively large molecules such as the lipids which we have previously reported. The project will not be constrained to evolutionary improvements in our present technique, however, as we propose substantive and revolutionary changes in approach, including microprocessor control and inclusion of state of the art microelectronics in the usual thermochemical hardware. Recent unpublished work on hydrogenation over platinum and rhodium catalysts has shown that these catalysts permit measurement of heats of hydrogenation of compounds which do not react on Pd catalyst. We propose to press the investigation into the area of polycyclic aromatic hydrocarbons, particularly those which are known or suspected carcinogens.